[LeetCode] Merge Two Sorted Lists

public class Solution {
    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
        
        if ( l1 == null && l2 == null) return null;
        else if (l1 == null) return l2;
        else if (l2 == null) return l1;
        
        ListNode head;
        head = (l1.val < l2.val) ? l1 : l2;
        
        ListNode now = new ListNode(0);
        ListNode head1 = l1;
        ListNode head2 = l2;
        
        while (head1 != null && head2 != null) {
            if ( head1.val < head2.val) {
                now.next = head1;
                head1 = head1.next;
            } else {
                now.next = head2;
                head2 = head2.next;
            }
            now = now.next;
        }
        
        if (head1 != null) now.next = head1;
        else now.next = head2;
        
        return head;
        
    }
}